(a) Field of the Invention
The present invention relates to a chemical mechanical polishing (CMP) apparatus and a CMP method using the same.
(b) Description of the Related Art
Recently, with the high integration of semiconductor devices, the structure thereof has been multi-layered. Accordingly, a polishing process for planarizing layers of a semiconductor wafer is typically included in a fabrication process of the semiconductor devices. As such a polishing process, a chemical mechanical polishing (CMP) process is widely adopted.
The CMP process is a process for polishing a surface of a wafer coated with an oxide or metal such as tungsten, copper, etc., by using mechanical friction as well as a chemical abrasive.
Here, mechanical polishing implies polishing a surface of the wafer using friction between a polishing pad and the surface of the wafer by rotating the wafer when it is fixed on a rotating polishing head, with the wafer pressed against the polishing pad (for example, made of polyurethane or polytex) that is attached on a platen of stainless steel or ceramic. In addition, chemical polishing implies polishing the surface of the wafer using slurry supplied between the polishing pad and the wafer as a chemical abrasive.
According to such a CMP process, in order to control polishing uniformity of the wafer, the rotation speed of the platen and/or the polishing head is controlled as is the pressure applied to the polishing head.
In addition, recent attempts have been made to improve the polishing uniformity by controlling the pressure applied to the polishing head such that the wafer may receive different pressures depending on zones.
However, such efforts to improve polishing uniformity have been satisfactory only to a limited degree, for the following reasons.
During the CMP process, heat is generated by the friction between a wafer and a polishing pad, and more heat is generated where a friction area is larger.
By measuring a temperature distribution using an infrared (IR) camera, a temperature of a central region of a wafer is found to be higher than a temperature of a peripheral region thereof, which is believed to be because the central region of the wafer has a wider friction area than does the peripheral region.
According to such a CMP process, the removal rate tends to increase as the temperature increases. Such a phenomenon results in a bigger difference in the removal rate between the central region and the peripheral region as the wafer becomes larger in diameter. Furthermore, planarization of a metal layer for forming a metal line produces greater frictional heat in comparison with planarization of an oxide layer, and in this case the polishing uniformity becomes worse.
In order to solve such a problem, attempts have been made to disperse the frictional heat by, for example, installing a coolant pipe in a platen, or by supplying slurries of different temperatures at multiple points. However, such a conventional method may only provide a mere effect of lowering the temperature of the platen, rather than enabling the temperature distribution of a wafer surface to be more uniform. Therefore, polishing uniformity that may be achieved by such a conventional method is not sufficient for an improvement of the polishing uniformity.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention, and therefore, it may contain information that does not form knowledge or prior art that may be already known in this or any other country to a person of ordinary skill in the art.